Thanks to a crit­i­cal fibre con­nec­tion in the brain (green), four-year-old kids can start to under­stand what oth­er peo­ple think. Cour­tesy of Max Planck Insti­tute.

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A remark­able mile­stone occurs in chil­dren around their fourth birth­days: They learn that oth­er peo­ple can have dif­fer­ent thoughts than they do. A recent study is the first to exam­ine the spe­cif­ic brain changes asso­ci­at­ed with this devel­op­men­tal break­through.

The new study specif­i­cal­ly explored the brain changes that occur when a child is able to rec­og­nize that anoth­er per­son believes some­thing that the child knows is false. Once chil­dren gain this abil­i­ty, they can bet­ter pre­dict oth­er people’s behav­ior and mod­i­fy their own—like deny­ing a wrong­do­ing that Mom didn’t see or help­ing out a friend who doesn’t know the rules of kick­ball.

Rec­og­niz­ing the false beliefs of oth­ers is a key step in devel­op­ing what psy­chol­o­gists call a the­o­ry of mind, the under­stand­ing that oth­er peo­ple may have dif­fer­ent thoughts, beliefs, inten­tions, or per­spec­tives.

“The­o­ry of Mind con­sti­tutes a key role for com­plex inter­ac­tion between human indi­vid­u­als, includ­ing behav­iors such as coop­er­a­tion, social com­mu­ni­ca­tion, and moral­i­ty,” write Char­lotte Grosse Wies­mann, Jan Schreiber, Tania Singer, Niko­laus Stein­beis, and Angela D. Friederi­ci of Lei­den Uni­ver­si­ty and the Max Planck Insti­tute in their Nature Com­mu­ni­ca­tions paper about the study.

To look for the brain changes that may under­lie a child’s devel­op­ment of a the­o­ry of mind, Grosse Wies­mann and col­leagues scanned the brains of 43 three- and four-year-old chil­dren using a tech­nique called dif­fu­sion-weight­ed mag­net­ic res­o­nance imag­ing (dMRI), which can detect the struc­ture and orga­ni­za­tion of white mat­ter with­in the brain.

White mat­ter is made up of nerve fibers that trans­mit mes­sages through­out the brain. It is white because it con­tains a fat­ty sub­stance called myelin that wraps around the nerve fibers, act­ing as an insu­la­tor to speed up neu­ronal mes­sages. Increas­es in myeli­na­tion cor­re­late close­ly with var­i­ous devel­op­men­tal mile­stones, but the growth of white mat­ter path­ways involved in the­o­ry of mind had not been explored in detail pri­or to this study.

In addi­tion to under­go­ing MRI scan­ning, the preschool­ers also per­formed two tasks that test­ed their abil­i­ty to think about the beliefs of oth­ers.

In the first task, the child and a mouse pup­pet were shown an emp­ty box and a lit­tle bag con­tain­ing a piece of can­dy. After the mouse left the room, the exper­i­menter moved the can­dy from the bag to the box. When the mouse reen­tered the room, the child was asked ques­tions about what the mouse would think about the loca­tion of the can­dy. Most three year olds said that the mouse thought the can­dy was in the box, where­as the four year olds were more like­ly to real­ize that the mouse would think the can­dy was still in the bag.

For the oth­er task, the child was shown a choco­late box that con­tained pen­cils. When a mouse pup­pet (who had been out­side) entered the room and encoun­tered the closed box, the child was asked what the mouse would think the box con­tained. Again, most three year olds assumed the mouse knew what they knew. They said that the mouse believed that the box con­tained pen­cils. The four year olds, how­ev­er, were more like­ly to real­ize that the mouse would believe that the choco­late box con­tained choco­lates.

So what was dif­fer­ent in the brains of the four year olds that allowed them to put them­selves in the mouse’s shoes, so to speak?

The researchers dis­cov­ered that mat­u­ra­tion of the white mat­ter fibers in a brain struc­ture called the arcu­ate fas­ci­cle was specif­i­cal­ly linked to the children’s abil­i­ty to rec­og­nize the mouse’s thoughts, but not to oth­er co-devel­op­ing cog­ni­tive skills (which were test­ed via oth­er tasks). These fibers con­nect parts of the tem­po­ral lobe, which is involved in pro­cess­ing oth­er people’s men­tal states in adults, with the medi­al pre­frontal cor­tex, a part of the frontal lobe that process­es abstract and hier­ar­chi­cal think­ing.

“Our find­ings show that the emer­gence of [the­o­ry of mind] is relat­ed to the mat­u­ra­tion of core belief pro­cess­ing regions and their con­nec­tion to the pre­frontal cor­tex,” write the authors.

While the researchers hypoth­e­size that con­nect­ing these two areas allows a child to build a men­tal rep­re­sen­ta­tion of oth­ers’ beliefs, future work will need to exam­ine the extent to which this rela­tion­ship is causal. One way to do this could be to scan the same chil­dren mul­ti­ple times to see whether devel­op­ment of the arcu­ate fas­ci­cle in an indi­vid­ual child pre­dates their abil­i­ty to rec­og­nize oth­ers’ false beliefs.

Intrigu­ing­ly, the authors note that non-human pri­mates have very weak arcu­ate fas­ci­cles. Great apes, like younger human tod­dlers, can pass some false-belief tasks, but they seem to lack the abil­i­ty to form more explic­it men­tal rep­re­sen­ta­tions of oth­ers’ false beliefs. This study may shine light on why, at least on a neur­al lev­el.

Indeed, the­o­ry of mind under­lies some of the best ele­ments of human­i­ty. Our abil­i­ty to show com­pas­sion and for­give­ness, to coop­er­ate and work towards com­mon goals, and to under­take moral rea­son­ing about what is right and wrong are all great­ly expand­ed by our capac­i­ty to con­cep­tu­al­ize how oth­er peo­ple think and feel. This study pro­vides new insights into how human brain devel­op­ment sets the stage for these essen­tial social skills and virtues.

Sum­mer Allen, Ph.D., is a sci­ence writer and fre­quent con­trib­u­tor to the Amer­i­can Asso­ci­a­tion for the Advance­ment of Sci­ence and to Greater Good. Based at UC-Berke­ley, Greater Good high­lights ground break­ing sci­en­tific research into the roots of com­pas­sion and altru­ism. Copy­right Greater Good.

The Study

Abstract: The abil­i­ty to attribute men­tal states to oth­er indi­vid­u­als is cru­cial for human cog­ni­tion. A mile­stone of this abil­i­ty is reached around the age of 4, when chil­dren start under­stand­ing that oth­ers can have false beliefs about the world. The neur­al basis sup­port­ing this crit­i­cal step is cur­rent­ly unknown. Here, we relate this behav­iour­al change to the mat­u­ra­tion of white mat­ter struc­ture in 3- and 4-year-old chil­dren. Tract-based spa­tial sta­tis­tics and prob­a­bilis­tic trac­tog­ra­phy show that the devel­op­men­tal break­through in false belief under­stand­ing is asso­ci­at­ed with age-relat­ed changes in local white mat­ter struc­ture in tem­poropari­etal regions, the pre­cuneus and medi­al pre­frontal cor­tex, and with increased dor­sal white mat­ter con­nec­tiv­i­ty between tem­poropari­etal and infe­ri­or frontal regions. These effects are inde­pen­dent of co-devel­op­ing cog­ni­tive abil­i­ties. Our find­ings show that the emer­gence of men­tal state rep­re­sen­ta­tion is relat­ed to the mat­u­ra­tion of core belief pro­cess­ing regions and their con­nec­tion to the pre­frontal cor­tex.

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